1. Field of the Invention
The invention relates to a power-supply device. More particularly, the invention relates to a power-supply device incorporating the function of converting an input voltage (such as an output voltage from an uninterruptible commercial power-supply device) and controlling an output voltage, or incorporating a series-parallel-type active filter or a control unit for controlling the flow of electric power, for example.
2. Background Art
First, as an example of the conventional art, the constitution of an uninterruptible commercial power-supply device is described below. The conventional art related to this power-supply device has been disclosed in Japanese Patent Publication (Laid-Open) No. JP 2001-128390. According to this patent document, the uninterruptible power-supply device consists of a series inverter functioning as a first voltage-supplying means, and a parallel compensatory capacitor functioning as a second voltage-supplying means. As described in paragraph [0004] of JP 2001-128390, by directly adding a compensatory output voltage from the first voltage-supplying means to an output voltage from the second voltage-supplying means, the output voltage is held at a rated value. In other words, by controllably operating a voltage output from the first voltage-supplying means, the above uninterruptible power-supply device advantageously keeps the output voltage constant, even when the input voltage varies. It is further possible to optionally vary the output voltage within a predetermined capacity of the above power-supply device.
Further, other conventional art is also known which, based on the principles cited above, properly compensates for the higher harmonic components of an output voltage when a voltage generated in an input power-supply line contains such higher harmonic components, by causing a first voltage-supplying means to generate a higher harmonic voltage containing the opposite phase. This conventional art is disclosed in the above-cited JP 2001-128390 and in Japanese Patent Publication (Laid-Open) No. JP 2001-161098.
As it is possible to vary the phases of the input and output voltages through the application of the first voltage-supplying means, the above art enables the realization of a phase-shifter. On the other hand, the flow of AC power can be controlled through the phase of the voltage, and thus the above art is also able to control the flow of AC power. The conventional art disclosed in both of the above-mentioned patent publications has been realized by combining the output voltage of the second voltage-supplying means or the input voltage at the input terminal with the output voltage of the first voltage-supplying means.